1. Field of the Invention
The present invention relates to a housing repair composition comprising a curable admixture of (1) a mixture of an epoxy resin/solvent/reactive diluent; (2) graphite powder; and (3) polytetrafluoroethylene powder. Moreover, the present invention is directed to a housing structure that has the cured form of the above admixture coated therein or applied into damaged or worn areas of the housing.
2. Brief Description of the Art
Aircraft fuel and oil pump housings requires repair because their gear drive bushings wear away during use. This wear (called xe2x80x9cgallingxe2x80x9d or xe2x80x9cscoringxe2x80x9d or xe2x80x9cgear wipingxe2x80x9d) limits the longevity of the pump housing and requires their replacement or their rebuilding.
One method of rebuilding such pump housing is disclosed in U.S. Pat. No. 4,996,085 which issued to Sievers on Feb. 26, 1991. That patent teaches coating the pump housing surfaces to be treated with a composition comprising a hardenable epoxy resin, a reinforcing filler, and an agent having a lower coefficient of friction than the epoxy resin. It is noted col. 2, lines 44-45, suggest that graphite may function as the reinforcing filler. Col. 3, lines 43-54, of the reference also teaches the frictional reducing agent may be graphite, in fibrous or granulated form; fluorinated carbon (i.e., xe2x80x94(CFx)xe2x80x94 wherein x less than 2); or molybdenum disulfide. It is noted that this reference does not provide any further specifics as to the fluorinated carbon materials useful for that invention. It is also noted that the preferred class of epoxy resins in this reference are diglycidyl ether of a dihydric phenol (e.g., the diglycidyl ether of bisphenol A).
A second method of treating such worn pump housing surfaces is disclosed in U.S. Pat. No. 5,316,790 which issued to Chan et al. on May 31, 1994. This patent describes a lubricative coating and filler material for restoring metal surfaces that have scratched, scored, grooved, or otherwise damaged to a functional condition. This coating and filler material is a mixture of an epoxy resin, tungsten disulfide, and isopropyl alcohol in a ratio of 9:1:1.6.
While these coating materials may be satisfactory for certain applications, there is still need for a better pump housing repair composition.
Accordingly, one aspect of the present invention is directed to a curable composition useful for repairing worn surfaces on housings comprising an admixture of:
(1) a mixture of (a) a least one one-component epoxy resin, (b) at least one solvent and (c) at least one reactive diluent, wherein said epoxy resin is present in a major (i.e. at least 50% by weight) amount in said mixture;
(2) graphite powder; and
(3) polytetrafluoroethylene powder.
Another aspect of the present invention is directed to a pump structure having the above-noted housing repair composition cured onto worn surfaces of the housing structure.
The preferred housing repair composition of the present invention comprises: (1) about 70% to about 90% by weight (more preferably 75% to about 88% by weight) of HYSOL SR1000 high solids epoxy resin/solvent mixture; (2) about 5% to about 15% by weight (more preferably, about 7% to about 13% by weight) of graphite; and (3) about 1% to about 10% by weight (more preferably, about 3% to about 8% by weight) of polytetrafluoroethylene powder.
HYSOL SR1000 is available from the Dexter Electronic Materials Division of the Dexter Corporation of Industry, Calif. This product contains diethylene glycol monoethyl ether acetate solvent (also known as carbitol acetate) [Chemical Abstract No. 000112152] as a solvent, as well as a bisphenol A epichlorohydrin polymer (a diglycidyl ether of bisphenol A) [Chemical Abstract No. 025068386] as an epoxy resin, and p-tert-butylphenyl glycidyl ether [Chemical Abstract No. 068958225] as a reactive diluent. The epoxy resin portion of this product constitutes a major portion (i.e., greater than 50% by weight) of the product. The epoxy resin used in this product is an one-component coatable-type epoxy resin. The term one-component as used herein means that the epoxy resin is pre-catalyzed and the term coating-type means a type other than adhesive-type epoxy resins. Small amounts of solvent will flash off during the curing process, causing little chance for voids in the rebuilt pump housing surface.
The preferred graphite powder is DCF graphite powder available from Graphite Sales, Inc. of Nova, Ohio.
Polytetrafluoroethylene powder, also known as TEFLON(trademark) powder, is a fluorinated carbon polymer of the formula xe2x80x94(CFx)xe2x80x94 where x=2.
The curable composition may also optionally contain color additives, metal powders or both. If it is desirable to use a metal powder, silver powder or copper powder in amounts from about 0.5% to 20% of the curable composition may be used.
The above mentioned three critical materials, as well as the optional ingredients, are preferably mixed together at ambient temperature under a vacuum to remove any air in the resulting paste. The paste may be then applied to either damaged or undamaged surfaces of a pump housing. When applied to the damaged surfaces, the paste acts as a filling and coating to the surface of the pump housing. When applied to the undamaged surfaces, it acts only as a coating to prevent future wear.
After being applied, the paste is cured by heating the paste and the pump housing part to which it is applied to suitable curing temperature for a sufficient amount of time. Suitable curing temperatures are from about 125xc2x0 to about 200xc2x0 C. The cured paste may then be machined to form a smooth surface on the pump structure. The curing and machining steps may be repeated several times to ensure that a completely cured and smooth surface results.
Besides its preferred use on pump housings, the curable composition of the present invention may also be used to repair worn housing parts on pistons, gear boxes, cover assemblies, valve bodies, actuators, cylinders, shafts and journals.
The following Examples are provided to better illustrate the present invention. All parts and percentages are be weight and all temperatures are degrees Celsius, unless explicitly stated otherwise.